Domain Name Resolution Resource Allocation

ABSTRACT

A content delivery network (CDN) for delivering content over the Internet is disclosed in one embodiment. The CDN is configured to deliver content for others and includes a domain resolution service (DNS) server, caching servers and an Internet interface. The DNS server receives a first domain resolution request and produces a first DNS solution, and receives a second domain resolution request and produces a second DNS solution. The first and second domain resolution requests correspond to a same domain. The caching servers correspond to a plurality of addresses. The interface receives domain resolution requests, which include the first and second domain resolution requests, and transmits DNS solutions, which include the first and second DNS solutions. The first DNS solution comprises a first plurality of addresses corresponding to at least a first subset of the plurality of caching servers, and the second DNS solution comprises a second plurality of addresses corresponding to at least a second subset of the plurality of caching servers. The first DNS solution is different from the second DNS solution in that the second subset includes an address for a caching server not in the first subset. The second subset is chosen to generally match a processing power of the first subset.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of and is a continuation-in-part ofco-pending U.S. patent application Ser. No. 11/284,493 filed on Nov. 21,2005, which is hereby expressly incorporated by reference in itsentirety for all purposes.

BACKGROUND

This disclosure relates in general to content delivery and, morespecifically, but not by way of limitation, to domain name service (DNS)resolution.

A content delivery network (CDN) is used by many web sites to delivercontent more efficiently. The CDN may host, mirror and/or cache thecontent as well as deliver it to a requesting party. A web site ororigin server is linked to the CDN such that some or all content can besourced from the CDN rather than the web site. This process offulfilling a link through a CDN is usually transparent to the user.

Singlecasting of large events can be difficult for CDNs to deliverefficiently. CDNs deliver content objects such as files or streams totens of thousands of recipients in a short period of time. Servingresources can be overwhelmed by these large events. Where a point ofpresence (POP) or individual servers saturate, a user can experienceinadequate quality of service (QoS). To avoid these bottlenecks, CDNsgenerally overbuild their serving resources and POPs. Overbuilding isundesirable, as it is inefficient and can result in increased expenseand complexity that is not needed during normal operating conditions.

A domain name service (DNS) is used to resolve the IP address or groupof IP addresses from where an object or stream should be sourced fordelivery to a recipient. Users' local DNS recursors participate in aseries of delegations to resolve the actual IP address of the serverthat will source the data. Through the delegation process, the requestfor data is routed to the server, which could be one of a number ofservers that could source the data.

One or more alternative server addresses can be provided during the DNSresolution process. Any of the alternative servers can be used toprovide the data associated with the requested domain. Where a smallnumber of server addresses is provided, and/or where each user DNSrecursor is given a DNS solution with the same server listed first,servers can overload and provide poor QoS. One solution to this problemis “round-robin DNS”, where IP addresses given in each DNS resolutionare the same, but the order of the IP addresses could be varied for eachDNS solution, with the goal of more evenly distributing the contentrequests across the servers.

Where a larger number of server addresses is desirable, there arelimits, typically encountered at user-network firewalls and othersecurity boundaries, on the size of a DNS solution packet, and thereforeon the number of IP addresses that can be included in such a solution. Atypical limit could be in the range of 16 to 20 IP addresses. There aretwo method known in the art that are usually deployed to work aroundthis limit and enable utilization of more servers than the limit of theDNS solution packet size. One method is to use a load balancing switchto virtualize the IP addresses. In this method, a small number oflogical IP addresses is returned in the DNS solution packet; contentrequests are intercepted by the load balancing switch; and the switchmaps those requests to a greater (often far greater) number of physicalIP addresses corresponding to physical servers. The switch is a “loadbalancing” switch because another of its functions, besides enabling thevirtualization of server addresses, is to balance loads across servers,which among other effects, normally makes round-robin DNS unnecessary(because even if all content requests came to a single logical IPaddress, the switch can distribute the load among the physical IPaddresses). Thus, in one example of this scenario, 16 logical IPaddresses are returned in each DNS solution; all content requests aredirected to one of these 16 logical IP addresses; the load balancingswitch translates the 16 logical IP addresses to 60 physical server IPaddresses; and the switch balances the loads across the 60 servers.

A second method of solving this DNS solution packet limit problem is todivide the content site into multiple, smaller logical sites, by usinghostnames for each portion of the site (a “hostname” is the portion ofthe URL to the left of the website name, e.g., in the URL img.foo.com,“img” would be the hostname). As an example, if foo.com requires morethan the limited number of servers that could be returned in a DNSsolution packet, it could be divided into part-A.foo.com,part-B.foo.com, and part-C.foo.com. When DNS resolutions are requested,different server addresses can be provided for each hostname, thereby(in this example), tripling the number of servers that can be used toserve the content. When using this method, round-robin DNS is stilluseful, because changing the order of the IP addresses presented in theDNS solution for part-A.foo.com can help to more evenly distribute thecontent requests across the servers. Both of these methods, however,have limitations.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is described in conjunction with the appendedfigures:

FIGS. 1A-1D are block diagrams of embodiments of a content system;

FIG. 2 is a block diagram of an embodiment of a content delivery network(CDN);

FIG. 3 is a block diagram of an embodiment of a point of presence (POP);

FIGS. 4A-4B are flow diagrams for embodiments of a process for issuing adomain name service (DNS) solution; and

FIG. 5 is a flow diagram of an embodiment of a process for dynamicallyadjusting server allocation to a domain serviced by the CDN.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The ensuing description provides preferred exemplary embodiment(s) only,and is not intended to limit the scope, applicability or configurationof the invention. Rather, the ensuing description of the preferredexemplary embodiment(s) will provide those skilled in the art with anenabling description for implementing a preferred exemplary embodimentof the invention. It being understood that various changes may be madein the function and arrangement of elements without departing from thespirit and scope of the invention as set forth in the appended claims.

Specific details are given in the following description to provide athorough understanding of the embodiments. However, it will beunderstood by one of ordinary skill in the art that the embodiments maybe practiced without these specific details. For example, circuits maybe shown in block diagrams in order not to obscure the embodiments inunnecessary detail. In other instances, well-known circuits, processes,algorithms, structures, and techniques may be shown without unnecessarydetail in order to avoid obscuring the embodiments.

Also, it is noted that the embodiments may be described as a processwhich is depicted as a flowchart, a flow diagram, a data flow diagram, astructure diagram, or a block diagram. Although a flowchart may describethe operations as a sequential process, many of the operations can beperformed in parallel or concurrently. In addition, the order of theoperations may be re-arranged. A process is terminated when itsoperations are completed, but could have additional steps not includedin the figure. A process may correspond to a method, a function, aprocedure, a subroutine, a subprogram, etc. When a process correspondsto a function, its termination corresponds to a return of the functionto the calling function or the main function.

Moreover, as disclosed herein, the term “storage medium” may representone or more devices for storing data, including read only memory (ROM),random access memory (RAM), magnetic RAM, core memory, magnetic diskstorage mediums, optical storage mediums, flash memory devices and/orother machine readable mediums for storing information. The term“machine-readable medium” includes, but is not limited to portable orfixed storage devices, optical storage devices, wireless channels andvarious other mediums capable of storing, containing or carryinginstruction(s) and/or data.

Furthermore, embodiments may be implemented by hardware, software,firmware, middleware, microcode, hardware description languages, or anycombination thereof. When implemented in software, firmware, middlewareor microcode, the program code or code segments to perform the necessarytasks may be stored in a machine readable medium such as storage medium.A processor(s) may perform the necessary tasks. A code segment mayrepresent a procedure, a function, a subprogram, a program, a routine, asubroutine, a module, a software package, a class, or any combination ofinstructions, data structures, or program statements. A code segment maybe coupled to another code segment or a hardware circuit by passingand/or receiving information, data, arguments, parameters, or memorycontents. Information, arguments, parameters, data, etc. may be passed,forwarded, or transmitted via any suitable means including memorysharing, message passing, token passing, network transmission, etc.

With reference to FIG. 1A, an embodiment of a content system 100 isshown where a content originator 106 offloads the delivery of thecontent objects to a content delivery network (CDN) 110. In oneembodiment, the content system 100 can dynamically adjust the allocationof server resources to content objects or streams to achieve a moreoptimal level of resources at any given level of demand. The contentoriginator 106 produces content object. Included in the contentoriginator 106 are a content provider 108 and a content origin site orweb site 116. A content object is any content file or content stream andcould include, for example, software, audio, video, pictures, data,and/or text. The content object could be live, delayed or stored. Thecontent site 116 can be located within the infrastructure of the contentprovider 108, within a CDN 110 and/or at an alternative location.Throughout the specification, reference may be made to a content object,content stream and/or content file, but it is to be understood thatthose terms could be used interchangeably wherever they may appear.

Many content providers 108 use a CDN 110 to deliver the content objectsto customers or recipients. When a content object is requested by arecipient, the CDN 110 retrieves the content object from the contentprovider 108. Alternatively, the content provider 108 may directlyprovide the content object to the CDN 110, i.e., in advance of the firstrequest. The CDN 110 then provides the content object to the recipient.The content provider 108 typically pays the CDN 110 for the delivery ofthe content object. In other embodiments, the CDN 110 could be captiveor associated with the content provider 108 such that payment is notperformed.

The content originator 106 is the source or re-distributor of contentobjects. The content site 116 is an Internet site accessible directly orindirectly via the Internet by the recipient computer 128. In oneembodiment, the content site 116 could be a web site where the contentis viewable with a web browser. In other embodiments, the content site116 could be accessible with application software other than a webbrowser and/or accessible from devices other than personal computers.Links on the content site 116 and/or links to individual content objectsare structured to allow delivery through one or more CDNs 110. The linksmay be rewritten before a web page is rendered or after a link isactivated by using a redirect.

The recipient computer 128 receives the content object and processes itfor the recipient. The recipient computer 128 could be a personalcomputer, media player, handheld computer, Internet appliance, phone, orany other device that can receive content objects. In some cases, therecipient computer 128 can be a number of computing devices that may benetworked together.

Each recipient computer or other device 128 is associated with anInternet service provider (ISP) 132. Each ISP 132 provides Internetconnectivity to one or more recipient computers or other devices 128.The ISP 132 may provide DNS caching in addition to any performed by therecipient computer or other device 128 and/or routers, gateways, orapplications. When a DNS solution is provided to any DNS cache atime-to-live period indicates when the particular solution is no longerto be used, such that a new DNS solution is requested to allow resolvinga particular domain. A recipient computer or other device 128 requestsand accepts the content objects for realization to the recipient. TheCDN 110 may be able to determine the particular ISP 132 associated witha particular recipient computer 128.

The content system 100 also includes a domain name service (DNS) server140, which is sometimes referred to as a “name server”. Resolving aparticular address for a particular server that would source aparticular content object is part of what the DNS server 140 allows.

With reference to FIG. 1B, another embodiment of the content system100-2 is shown where a content originator 106 offloads the delivery ofthe content objects or streams to a captive CDN 110-1. In the embodimentof FIG. 1A, the CDN 110 is a third party with respect to the contentoriginator 106. In this embodiment, the captive CDN 110 is associatedwith the content originator 106 and selectively used to deliver contentobjects. For a captive CDN 110, the functions of the CDN 110 could becombined with and/or divided from other functions of the contentoriginator 106. Portions of the captive CDN 110 could be integrated intothe content provider, for example, or vice versa.

Referring next to FIG. 1C, yet another embodiment of the content system100-3 is shown where a content originator 106 can choose to offload thedelivery of the content objects or streams to either a captive CDN 110-1or an external CDN 110-2. Routing algorithms are used to choose betweenthe two CDNs 110. Various domains of the content originator 106 coulddivided between the two or more CDNs 110. For example, a domain assignedto an external CDN 110-2 such that all requests were serviced from thatCDN 110-2, while other domains are serviced by the captive CDN 110-1.

With reference to FIG. 1D, still another embodiment of the contentsystem 100-4 is shown where multiple content originators 106 are shown.Typically, an external CDN 110 operates with multiple domains for themultiple content originators 106. In embodiments with a captive CDN 110may also have a number of domains that are associated with theassociated content originator 106. The DNS server 140 resolves domainsof the content originators 106 into server IP addresses.

Referring next to FIG. 2, a block diagram of an embodiment of a CDN 110is shown. The CDN 110 could be captive or external in this embodiment. Anumber of Points of Presence (“POPs”) 204 are associated with the CDN110 and could source multiple domains. Some domains may be sered by onlycertain POPs 204 unless the original POP(s) 204 become(s) overwhelmed.Generally, the POPs 204 are geographically dispersed across theInternet.

Content originators 106 can be manually assigned to one or more POPs204, or could be assigned to one or more POPs 204 automaticallyaccording to a determination by an automated POP resource manager 216.The POP resource manager 216 function could be located at one site ordistributed to multiple sites, including to every POP 204 in the CDN.The server resources, capacity, and activity of POPs 204 may be takeninto account during content originator 106 assignment in someembodiments. As the server resources at a POP 204 become fully assignedand or as activity, or a specific subset of activity, at the POP 204rises to a level that exceeds defined thresholds, the POP resourcemanager 216 can help the high activity POP 204 provide DNS solutionsthat include content server resources from other POPs 204.

A WAN 220 allows communication among the POPs 204 and between the POPs204 and the POP resource manager 216. The WAN 220 can transportinformation faster than the Internet 104 in many instances. Serveravailability and health checks (operating characteristics), as well asactivity levels associated with specific content originators 106,content objects, or domains can be communicated between the POPs 204and/or monitored by the POP resource manager 216 by way of the WAN 220.When one POP 204 communicates with another POP 204, the WAN 220 can beutilized for this communication. For example, one POP 204 coulddetermine activity levels or resource utilization of other POPs 204 bydirect communication or by getting a report from the POP resourcemanager 216 or POP resource managers 216 in other POPs 204.

With reference to FIG. 3, a block diagram of an embodiment of a POP 204is shown. The POP 204 sources the content objects from any number ofcontent servers 308. Each content server 308 has a data cache 312 inthis embodiment, but other content servers 308 could host domainswithout caching such that content objects are not dynamically associatedor disassociated with the content server 308. Where the content server308 doesn't have a requested content object stored on the data cache312, the content object could be requested from another content server308 in the POP 204, in another POP 204 or the origin server of thecontent originator 106. After the request, the content object is storedon the data cache 312 until inactivity or other caching algorithms pushthe content object from the data cache 312.

The POP 204 uses at least three types of networks in this embodiment,specifically, the Internet 104, a WAN 220 and a LAN 304. Generally, theLAN 304 is for communication within the POP 204, the Internet 104 is forreceiving domain resolution requests and content object requests and theWAN 220 is for communication within the CDN 110. The WAN 220 could beimplemented via the Internet, using such techniques as tunneling orvirtual private networking, or simply by utilizing standard Internetcommunications protocols. Where a particular POP 204 doesn't have arequested content object stored, it may be requested from another POP204 over the WAN 220. Should the missing content object not be stored onanother POP 204, the content object can be requested from the contentoriginator 106.

A POP DNS server 340 receives the domain resolution requests. The POPDNS 340 resolves a particular domain to a particular IP address or groupof IP addresses in a DNS solution, where each IP address is for aserver(s) that can source the content object. The POP DNS server 340returns IP addresses of one or more content servers 308 in this oranother POP 204 of the CDN 110. A particular DNS solution typicallyprovides a number of content server IP addresses available to serve aparticular domain along with a time-to-live for the DNS solution (e.g.,2 minutes, 5 minutes, 10 minutes, 30 minutes, 1 hour, 5 hours, etc.). Aparticular IP address will generally correspond to a single server, butmay correspond to a group of servers accessible from that IP address.

During the DNS resolution, the POP DNS server 340 determines theappropriate number of content servers 308 to be assigned based on thecontent originator 106, the domain being resolved, the specific contentobject requested, and/or other factors. The appropriate number ofcontent servers 308 to use in a particular DNS solution in variousembodiments is based on the total number of content servers 308available at the POP 204 or alternatively at the POP 204 and one or moreof the other POPs 204, the overall level of activity associated with thecontent originator 106, the particular domain being resolved, and/or thespecific content object requested.

In one embodiment, the appropriate number of content servers 308 is thesmallest number, or smallest choice of specific number from a list ofvalues such as 4, 8, 16, etc., that is deemed to be sufficient toservice the overall level of activity associated with the contentoriginator 106, the domain being resolved, or the specific contentobject requested, such that the number of content servers 308 issufficient and that the storage of the content object(s) and/orutilization of the content servers 308 is concentrated on a specificnumber of all of the content servers 308 in the POP 204. Typically, theconcentration on a specific number of all the content servers 308 isless than all available at the POP 204. As the overall level of activityassociated with the content originator 106, the domain being resolved,or the specific content object requested changes, the number of contentservers 308 may change either smoothly (e.g., one at a time) or in steps(e.g., four at a time). The appropriate number of content servers 308may be determined periodically and stored in a table for look-up at eachDNS resolution or may be dynamically calculated for each DNS resolution.As the appropriate number of content servers 308 is determined, the POPDNS server 340 maintains a list of that number of specific contentservers 308, such that the specific content server 308 IP addresses willbe returned in that and future DNS resolutions associated with thatspecific content originator 106, domain being resolved, or specificcontent object. In this way, the DNS solutions can be assigned to thesame specific group of servers or a subset from that group.

The POP DNS server 340 also monitors each content server's 308availability and health, typically by simulating a content objectrequest and measuring the server's response time to determine if theserver is operating properly. If the POP DNS server 340 determines thata specific content server 308 has failed or is not operating properly,the POP DNS server 340 can permanently or temporarily delete thatspecific content server 308 from all lists of specific content servers308 on which it appears, and replace it on each list of content servers308 with another content server 308, if one is available. Differentlists may receive different replacement content servers 308. Based uponthese analyses and steps, for example, more content server IP addressescould be provided in response to a given DNS resolution request; morecontent server IP addresses could be selected from a universe of morecontent servers for that particular object; and/or IP addresses ofinoperative or poorly-operating content servers could be avoided.

In finally providing a DNS resolution (i.e., a DNS solution set), thePOP DNS server 340 does not necessarily return all the IP addresses forall content servers 308 that are on the list for a given DNS resolution.In many cases, a subset of the IP addresses from the list is returned,for example, in order that the data size (e.g., IP packet size) of theDNS solution is not larger than is desirable. In cases where the POP DNSserver 340 determines that it will return a DNS solution set that isless than all of the IP addresses on the list, the selection of IPaddresses from the list can be done randomly, by rotating solutionsthrough the list in round robin fashion ,or can be based on othercriteria, such as server load level. Once the DNS solution set isdetermined, the sequence of the IP addresses that is returned will berandomized or “shuffled” in one embodiment. Each time a DNS resolutionis performed for a given content originator 106, domain, or specificcontent object in other embodiments, the sequence of the IP addressesmay be varied in some other fashion, or may not be varied at all.

Each POP 204 can have multiple POP DNS servers 340. In one embodiment,each POP DNS server 340 can perform all of the requisite POP DNS server340 functions during domain resolution, such that the POP DNS server 340can complete the entire DNS resolution process without delegating orassigning any of the DNS resolution process to another POP DNS server340. In other words, when a POP DNS server 340 is used, that POP DNSserver 340 handles a given domain name resolution request from start tofinish once received. If there is more than one POP DNS server 340 at agiven POP 204, the various POP DNS servers 340 can be allocated tosubsets of the domains served in this embodiment, with a degree ofoverlap that provides redundancy in the event that a specific POP DNSserver 340 fails. In other embodiments, DNS resolution requests can bedistributed randomly among the POP DNS server 340 s in the POP 204, in around-robin fashion or according to some other distribution scheme, orthere can be a combination of domain assignments and random orround-robin distribution of requests. The POP DNS servers 340 in a givenPOP 204 are synchronized and work in concert to share the DNS resolutionrequest load for the POP 204 in this embodiment. The POP DNS servers 340in multiple POPs 204 may also be synchronized and work in concert. Forredundancy, the number of POP DNS servers 340 is two or more in oneembodiment, but is typically greater than two to improve QoS in someembodiments.

Content object requests are ultimately served by a content server 308associated with an IP address presented in the DNS solution to therecipient computer 128. The ISP 132 and/or recipient computer 128 candirect a content object request to any content server 308 IP address inthe DNS solution. The chosen content server 308 provides the contentobject to the recipient computer 128. The content server 308 can be asingle server or group of servers associated with the IP address.

In one embodiment, the DNS solution is limited to x content server IPaddresses. A particular domain, content originator and/or content objectis allocated a number of particular content servers 308, y. Theallocation is dependent on the activity level associated with thedomain, contract origiator and/or content object and, optionlly,theassociated serice level. Allocation may be increased by additionalallocation of one or more content servers. Those y content servers 308may be more or less than x. Where y is less than x, all y contentservers 308 are used in each DNS solution. Where a particular allocatedcontent server 308 becomes unhealthy, poorly-operating, or utilizedbeyond a threshold, it can be deleted from the allocation, and anothercontent server 308, if available, could be allocated in its place. ThePOP DNS 340 also knows the “starting point” for server allocations, andknows which servers have the appropriate resources and/or capabilitiesavailable, and can match these to those needed for a particular domainprior to allocation. This embodiment allocates based upon domain, butother embodiments could allocate based upon content originator orcontent object.

Table I shows allocation of twelve content domains among twelve contentservers 308 for a particular POP 204. Some of the domains are allocated4, 8 or 12 content servers 308 in this embodiment. Allocation isstaggered for a particular domain such that the content servers 308serving one domain are unlikely to be all of the content servers 308 foranother domain. TABLE I Server Allocation Example Domain AllocatedServers ACME.org y₁, y₂, y₃, y₄ ABC.eu y₃, y₄, y₅, y₆ XYZ.com y₅, y₆,y₇, y₈, y₉, y₁₀, y₁₁, y₁₂ AAA.tv y₇, y₈, y₉, y₁₀ ZZZZZ.in y₉, y₁₀, y₁₁,y₁₂ FOO.iq y₁, y₂, y₃, y₄, y₅, y₆, y₇, y₈, y₉, y₁₀, y₁₁, y₁₂ AQME.comy₁, y₂, y₃, y₄ AABBCC.cn y₁, y₂, y₃, y₄, y₅, y₆, y₇, y₈ JONSMITH.net y₅,y₆, y₇, y₈ FOOFOO.org y₇, y₈, y₉, y₁₀ EXAMPLE.biz y₁, y₂, y₁₁, y₁₂USPPC.gov y₁, y₂, y₃, y₄, y₅, y₆, y₇, y₈, y₉, y₁₀, y₁₁, y₁₂

The activity level associated with the content originator 106, thedomain being resolved, or the specific content object requested can bedetermined by the POP DNS server 340 based upon the number of contentobject requests, amount of bandwidth, number of content objects, orother metrics. Activity level for a domain on a particular contentserver 308 is used in this embodiment, but other embodiments coulddetermine activity for a content originator or content object also. Thegranularity of the activity level could be per software service(s),hardware component(s), server(s), or pop(s) in various embodiments.

Resource utilization can be measured by the content server 308 andreported to the POP DNS server 340 periodically or if a threshold iscrossed. For example, resources such as CPU utilization, diskinput/output, memory utilization, number of connections, number ofrequests or other metrics can be monitored and reported; these metricscan be used by the POP DNS server 340 in determining whether the contentserver 308 is operating properly or operating poorly; alternatively, oradditionally, the POP DNS server 340 can monitor each content server's308 availability and health by simulating a content object request andmeasuring the server's response time to determine if the server isoperating properly. Table II shows how the POP DNS server 340 couldreallocate content servers after a content server 308 y₅ is removed fromthe future DNS solutions after the POP DNS server 340 has determinedthat the content server 308 y₅ is no longer available or operatingproperly.

In this example, other content servers 308 are allocated to replace y₅308 in a staggered manner such that content server 308 y₅ is notreplaced by a single (i.e., the same) content server 308 in everyallocation in which it had formerly appeared. In this embodiment, theFOO.iq and USPPC.gov domains lose one content server 308 from theirallocation when y₅ goes down. Other embodiments could allocate anothercontent server 308 from another POP 204 such that the number of contentservers 308 in the allocation remains unchanged, but with the resultthat potentially some of the content requests of some recipientcomputers 128 are serviced entirely or in part by a content server 308located in another POP 204. TABLE II Server Allocation Example AfterDeallocation of y₅ Domain Allocated Servers ACME.org y₁, y₂, y₃, y₄ABC.eu y₃, y₄, y₆, y₇ XYZ.com y₁, y₆, y₇, y₈, y₉, y₁₀, y₁₁, y₁₂ AAA.tvy₇, y₈, y₉, y₁₀ ZZZZZ.in y₉, y₁₀, y₁₁, y₁₂ FOO.iq y₁, y₂, y₃, y₄, y₆,y₇, y₈, y₉, y₁₀, y₁₁, y₁₂ AQME.com y₁, y₂, y₃, y₄ AABBCC.cn y₁, y₂, y₃,y₄, y₆, y₇, y₈, y₉ JONSMITH.net y₆, y₇, y₈, y₉ FOOFOO.org y₇, y₈, y₉,y₁₀ EXAMPLE.biz y₁, y₂, y₁₁, y₁₂ USPPC.gov y₁, y₂, y₃, y₄, y₆, y₇, y₈,y₉, y₁₀, y₁₁, y₁₂

When a new content server 308 is added to DNS solutions for a particulardomain, that new server 308 may be moved to being the first listedaddress in the DNS solutions for a period of time, to load up thecontent server 308 with content and/or activity for that domain. The POPDNS 340 can stop favoring the new content server 308 after under a loadcommensurate with other content servers 308.

From the viewpoint of a particular content server 308, it can beincluded in any number of DNS solution functions performed by the POPDNS server 340. For example, server y₂ is allocated to resolutionrequest processes for the ACME.org, FOO.iq, AQME.com, AABBCC.cn,EXAMPLE.biz, and USPPC.gov domains. Each domain has its own DNS solutionfunction that is varying DNS solutions per domain. That is to say, aresolution request to any of these domains may or may not include y₂ atthe top of the list. Further, any number of different files of differentsizes may be associated with each of the allocated domains. In this way,a particular content server 308, y₂, is included in any number of DNSsolution functions for different domains in varying orders. This canunpredictably spread the object requests among a group of contentservers 308.

A particular content server 308 can be taken offline in a permanent ortemporary manner. Permanent removal may be caused by a failure of thecontent server 308 that may be repaired and brought online at anothertime. Temporary removal may be preferable when the content server 308has not failed outright, but rather is operating poorly and may returnto operating properly in time. For example, if the POP DNS server 340has used a memory utilization measurement reported by the content server308 to conclude that the content server 308 is no longer operatingproperly, that memory utilization level may drop in time as theprocess(es) causing the abnormally high memory utilization is(are)terminated by the operating system, terminated by an application orprogram, or end naturally. When temporary removal is caused by autilization measurement exceeding a first threshold, an equal or lowersecond threshold is used to determine when to start using the contentserver 308 again in DNS solutions in this embodiment. Use of twothresholds, with the second threshold lower than the first, preventsutilization from oscillating around a single threshold that would cyclebetween an additional number of servers being included in new DNSsolutions and then not included.

The DNS solution can be varied from one domain resolution request to thenext such that various ISPs 132 receive a different ordered list ofcontent servers 308. The DNS solutions may be varied in a round robin orrandom fashion such that the first content server 308 is likely to bedifferent. For example, resolving AQME.com may result in a firstsolution, s₁, of y₁, y₂, y₃, y₄ and a second solution, s₂, of y₂, y₃,y₄, y₁, where the difference is a circular shift or round robin. Inanother example, s₁=y₄, y₂, y₃, y₁ and s₂=y₁, y₃, y₄, y₂ such thatsolutions vary in a random, pseudorandom or unpredictable manner.

As mentioned above, the number of server addresses can be limited in asolution, i.e., x<y. In various embodiments, x may equal 32, 16, 8, or4. Referring back to Table I, the domain FOO.iq has twelve possiblecontent servers 308 to choose from, but in this example, the solutionsize is limited to five. For each DNS solution, five of the twelvepossible content servers 308 are chosen for inclusion in a random orround-robin fashion. For example, s₁=y₁, y₂, y₃, y₄, y₅ and s₂ =y₂, y₃,y₄, y₅, y₆, could be chosen in way that varies in a round-robin fashion.

Some embodiments take into account the processing power for the contentservers 308 in allocating and reallocating them to a particulardomain(s). The DNS solution may allocate more or less content serversbased upon their ability to serve requests. For example, a first contentserver may have a single processor capable of serving one millionrequests per hour, and a second content server may have dual processorscapable of serving two million requests per hour. In any event, theseembodiments take some figure(s) of merit to estimate processing powerand allocate servers based upon the figure(s) of merit. In Table IIIa,the actual servers are translated to equivalent servers using a functionof the number of processors and/or processor cores. The function here isthat the first processor is equivalent to a server, but each additionalprocessor only adds a half server. For example, a two-processor computerwould equal one and one-half equivalent servers. The embodiment of TableIIIa allocates the servers according to Table IV. TABLE IIIa ServerProcessing Power Server Processors Equivalent Servers y₁ 1 1 y₂ 2 1.5 y₃2 1.5 y₄ 4 2.5 y₅ 2 1.5 y₆ 1 1 y₇ 1 1 y₈ 1 1 y₉ 8 4.5 y₁₀ 1 1 y₁₁ 4 2.5y₁₂ 6 3.5

There are any number of ways to determine how particular serverstranslate into a number of equivalent servers. The embodiment of TableIIIb tests each server or monitors its activity during normal use todetermine the number of transactions that can be processed over a giventime period. The ability to handle transactions correlates to the numberof equivalent server. For example, number of equivalent servers is equalto the number of times that 10,000 transaction that can be handled in asecond. The embodiment of Table IIIc uses a number of factor thatchacterize the server to find the number of equivalent servers, forexample, number of procesors, amount of memory, number of encoders,processor speed. TABLE IIIb Server Processing Power Server TransactionsEquivalent Servers y₁ 12,000 1.2 y₂ 21,000 2.1 y₃ 24,000 2.4 y₄ 39,0003.9 y₅ 20,000 2.0 y₆ 8,000 0.8 y₇ 17,000 1.7 y₈ 12,000 1.2 y₉ 80,000 8.0y₁₀ 11,000 1.1 y₁₁ 43,000 4.3 y₁₂ 35,000 3.5

The determination of which servers in a DNS solution can be simplifiedin some embodiment. For example, the DNS solution could use 16 serverswhere half are multi-processor and half are single-processor. Should oneof the servers become unavailable or begin operating poorly, anotherserver of the same type would be chosen to replace it, for example, adual-processor server would be replaced with another dual-processor. Thereplacement server(s) are chosen to generally match the processing powerof the unavailable or poorly operating server. For example, theequivalent servers of the unavailable or poorly operating server mayequal 1.5, but the replacement server may be ranked at 1.7 equivalentserver. Some embodiments randomly select servers of differentconfigurations, and randomly pick a replacement when one becomesunavailable. In another embodiment, each DNS solution might include aminimum of one type of server, for example, the DNS solution wouldinclude at least four dual-processor servers that have at least oneencoder. TABLE IIIc Server Processing Power Equivalent Server ProcessorsSpeed Memory Encoders Servers y₁ 1 2 GHz 1 GB 0 1.2 y₂ 2 1 GHz 4 GB 42.4 y₃ 2 1 GHz 2 GB 3 2.4 y₄ 4 2 GHz 8 GB 2 3.9 y₅ 2 5 GHz 2 GB 2 2.0 y₆1 4 GHz 1 GB 2 1.1 y₇ 1 2 GHz 1 GB 2 1.5 y₈ 1 2 GHz 2 GB 4 1.5 y₉ 8 3GHz 7 GB 3 8.0 y₁₀ 1 4 GHz 1 GB 1 1.5 y₁₁ 4 2 GHz 5 GB 5 4.3 y₁₂ 6 1 GHz8 GB 8 3.5

TABLE IV Server Allocation Based Upon Processing Power Domain EquivalentServers Allocated Servers ACME.org 4 y₁, y₂, y₃ ABC.eu 4 y₂, y₃, y₆XYZ.com 8 y₃, y₄, y₅, y₁₁ AAA.tv 4 y₄, y₅ ZZZZZ.in 4 y₅, y₁₁ FOO.iq 12y₆, y₇, y₈, y₉, y₁₀, y₁₁, y₁ AQME.com 4 y₇, y₈, y₁₀, y₁ AABBCC.cn 8 y₈,y₉, y₁₁ JONSMITH.net 4 y₁₀, y₂, y₃ FOOFOO.org 4 y₁₁, y₂ EXAMPLE.biz 4y₁, y₂, y₃ USPPC.gov 12 y₉, y₁₂, y₁, y₂, y₃, y₆, y₇

Referring next to FIG. 4A, a flow diagram of an embodiment of a process400-1 for issuing a DNS solution is shown. The depicted portion of theprocess 400-1 begins in step 404 where the POP 204 receives a request toresolve a domain. The POP DNS 340 does analysis on the request, therecipient computer and ISP locations and possibly, the other POPs 204before indicating which servers should be included in the DNS solution.

A step 428, which includes sub-steps 416, 420 and 424, is performednext. In sub-step 416, they server addresses that are allocated to therequested domain are determined. This may be done by simply countingservers or by counting equivalent servers. When counting equivalentservers, the processing power may not match exactly, but it generallymatches in one embodiment. Any servers 308 determined to be unavailableare removed from the list of possible servers in sub-step 420. Insub-step 424, servers 308 that are determined to be operating poorly arealso removed from the list of possible servers. Replacements for theremoved server may be randomly chosen or to match the processing powerof the removed server. Upon completion of step 428, the set of possibleservers that could be used in a DNS solution are known.

In step 432, a determination is made to see if the number of possibleservers exceeds the solution limit, i.e., is y<x? If that is the case,the set of possible servers is reduced in step 436 in a manner wheredifferent servers are culled over time. Where the limit is not exceededin step 432 or after culling occurs in step 436, the list of servers isarranged in a mixed-up or round-robin fashion in step 440. Atime-to-live value is determined or retrieved for adding to the DNSsolution in step 444. In step 448, the DNS solution is delivered to theDNS recursor.

With reference to FIG. 4B, a flow diagram of another embodiment of aprocess 400-2 for issuing a DNS solution is shown. In comparison to theembodiment of FIG. 4A, this embodiment adds steps 434 and 436 betweensteps 432 and 440. If it is determined in step 432 that there are morepossible servers in the set than afforded by the solution limit,processing goes to step 434 where a further determination is made to seeif the number of servers in the set is less than the allocation for aparticular domain. Where the allocation is complied with processingcontinues to step 440. In the alternative case, more servers are addedfrom a remote POP 204. Those remote servers are added in step 436 to thelist of possible servers before processing continues to step 440.

Referring next to FIG. 5 is a flow diagram of an embodiment of a process500 for adjusting server allocation to a domain serviced by the CDN 110.The depicted portion of the process 500 begins in step 504 where aninitial allocation is made for a set or list of servers 308 that cancache or store content objects for the domain. In step 508, the specificactivity level for the domain across the allocated servers 308 isdetermined.

Where the activity level is above the first threshold, the allocation isincreased in step 524. If the activity level was not above the firstthreshold in step 516, processing would continue to step 520 todetermine if the activity level was below a second threshold. In theevent that the activity level was below the second threshold, theallocation would be decreased in step 528.

Although some of the above embodiments talk in terms of reaching aspecific activity level, before increasing content server 308 allocationor including content servers 308 from other POPs 204. These actionscould be done far before the maximum activity level for a content server308 or a POP 204 is reached. For example, inclusion of content servers308 from other POPs 204 could begin at any threshold such as 30%, 40%,50%, 60%, 70%, or 80% of the maximum activity level.

Some of the above block diagrams mention a server or block that performsa function. That server or block may be implemented with a single ormultiple servers. Where multiple servers are used, they may begeographically spread out, but function as a single unit from someperspectives. For example, the POP DNS server 304 may be one serverco-located with the POP 204, could be multiple servers located in thePOP 204 or could be a geographically diverse set of servers accessiblefrom the POP 204. As those skilled in the art appreciate, networks allowvaried configurations while still implementing the same function.

Some of the embodiments are discussed in relation to CDNs, but the wayDNS solutions are determined is applicable to any system that providesalternative addresses for a domain. The DNS solution with thealternative addresses could be provided by the content originator incases where there is a captive CDN or no CDN at all.

While the principles of the disclosure have been described above inconnection with specific apparatuses and methods, it is to be clearlyunderstood that this description is made only by way of example and notas limitation on the scope of the invention.

1. A content delivery network (CDN) for delivering content over theInternet, wherein the CDN is configured to deliver content for others,the CDN comprising: a domain resolution service (DNS) server, wherein:the DNS server is configured to receive a first domain resolutionrequest and produces a first DNS solution, the DNS server is configuredto receive a second domain resolution request and produces a second DNSsolution, and the first and second domain resolution requests correspondto a same domain; a plurality of caching servers, wherein the pluralityof caching servers correspond to a plurality of addresses; and aninterface with the Internet, wherein: the interface is configured to:receive a plurality of domain resolution requests, and transmit aplurality of DNS solutions, the plurality of DNS solutions comprise thefirst and second DNS solutions, the plurality of domain resolutionrequests comprise the first and second domain resolution requests, thefirst DNS solution comprises a first plurality of addressescorresponding to at least a first subset of the plurality of cachingservers, the second DNS solution comprises a second plurality ofaddresses corresponding to at least a second subset of the plurality ofcaching servers, the first DNS solution is different from the second DNSsolution in that the second subset includes an address for a cachingserver not in the first subset, and the second subset is chosen togenerally match a processing power of the first subset.
 2. The CDN fordelivering content over the Internet as recited in claim 1, wherein thefirst subset has fewer of the plurality of caching servers than areavailable in the plurality of DNS solutions for the domain.
 3. The CDNfor delivering content over the Internet as recited in claim 1, whereinthe DNS server and the plurality of caching servers are at least part ofa point of presence (POP).
 4. The CDN for delivering content over theInternet as recited in claim 1, wherein: the first and second DNSsolutions list common addresses in the first and second subsets in adifferent order; and the different order varies in at least one of amixed-up fashion, a round-robin fashion or a random fashion.
 5. The CDNfor delivering content over the Internet as recited in claim 1, furthercomprising a wide area network coupling the plurality of caching serverstogether, wherein at least one of the plurality of caching servers isgeographically remote from the others in the plurality of cachingservers.
 6. The CDN for delivering content over the Internet as recitedin claim 1, wherein: the DNS server, the plurality of caching servers,and the interface are at least part of a POP; the POP is one of aplurality of POPs; and at least some of the plurality of POPs aregeographically separated.
 7. The CDN for delivering content over theInternet as recited in claim 1, wherein the first and second DNSsolutions choose their servers from a same subset of the plurality ofcaching servers.
 8. The CDN for delivering content over the Internet asrecited in claim 1, wherein the DNS server and caching servers aregeographically co-located.
 9. The CDN for delivering content over theInternet as recited in claim 1, wherein: at least one of the pluralityof caching servers is implemented with a plurality of computers; and theat least one corresponds to a single address in a DNS solution.
 10. TheCDN for delivering content over the Internet as recited in claim 1,wherein: the processing power is determined using one or more figures ofmerit; and the one or more figures of merit characterize the pluralityof caching servers in a subset.
 11. A method for delivering content overthe Internet, wherein the method comprises: receiving a first domainresolution request; producing a first DNS solution corresponding to thefirst domain resolution request; returning the first DNS solution;receiving a second domain resolution request; producing a second DNSsolution corresponding to the second domain resolution request; andreturning the second DNS solution, wherein: the first and second domainresolution requests correspond to a same domain or content originator, aplurality of servers corresponding to a plurality of addresses, thefirst DNS solution comprises a first plurality of addressescorresponding to at least a first subset of the plurality of servers,the second DNS solution comprises a second plurality of addressescorresponding to at least a second subset of the plurality of servers,the first plurality of addresses includes at least one address that isdifferent from the second plurality of addresses, and the second subsetis chosen to generally match a processing power of the first subset. 12.The method for delivering content over the Internet as recited in claim11, further comprising a step of determining that at least one of thefirst plurality of addresses should be removed from further DNSsolutions, wherein the second DNS solution does not include the one. 13.The method for delivering content over the Internet as recited in claim11, wherein the first subset is chosen from a larger number of serversthat could be selected for DNS solutions.
 14. The method for deliveringcontent over the Internet as recited in claim 11, wherein the firstsubset is smaller than the second subset.
 15. A machine-readable mediumhaving machine-executable instructions for performing themachine-implementable method for delivering content over the Internet ofclaim
 11. 16. A system adapted to perform the machine-implementablemethod for delivering content over the Internet of claim
 11. 17. Amethod for delivering content over a network, wherein the methodcomprises: receiving a first domain resolution request; determining aset of a plurality of servers allocated to a domain; producing a firstDNS solution corresponding to the first domain resolution request;returning the first DNS solution; receiving a second domain resolutionrequest; producing a second DNS solution corresponding to the seconddomain resolution request; and returning the second DNS solution withthe network interface, wherein: the first and second domain resolutionrequests indicate the domain, the plurality of servers corresponding toa plurality of addresses, the first DNS solution comprises a firstplurality of addresses corresponding to at least a first subset of theset, the second DNS solution comprises a second plurality of addressescorresponding to at least a second subset of the set, the first DNSsolution includes an address absent from the second DNS solution, andthe second subset is chosen to generally match a processing power of thefirst subset.
 18. The method for delivering content over the network asrecited in claim 17, wherein the network interface and the plurality ofservers are geographically collocated.
 19. The method for deliveringcontent over the network as recited in claim 17, wherein the first andsecond subsets generally match when a number of processing cores isequal.
 20. A machine-readable medium having machine-executableinstructions for performing the machine-implementable method fordelivering content over the network of claim
 17. 21. A content deliverynetwork (CDN) for delivering content over the Internet, wherein the CDNis configured to deliver content for others, the CDN comprising: aplurality of caching servers, wherein the plurality of caching serverscorrespond to a third plurality of server addresses, wherein: a firstplurality of server addresses are a first subset of the third pluralityof server addresses, a second plurality of server addresses are a secondsubset of the third plurality of server addresses, and the thirdplurality of server addresses are used in DNS solutions; an interfacewith the Internet, wherein the interface is configured to: receive aplurality of domain resolution requests, and transmit a plurality of DNSsolutions corresponding to the plurality of domain resolution requests;a first DNS solution function associated with a first domain, wherein:the first DNS solution function produces a first plurality of DNSsolutions corresponding to the first domain, the first plurality of DNSsolutions are different from each other, and each of the first pluralityof DNS solutions comprises at least some of the first plurality ofserver addresses; and a second DNS solution function associated with asecond domain, wherein: the second DNS solution function produces asecond plurality of DNS solutions corresponding to the second domain,the second plurality of DNS solutions are different from each other, andeach of the second plurality of DNS solutions comprises at least some ofthe second plurality of server addresses.
 22. The CDN for deliveringcontent over the Internet as recited in claim 21, wherein a serveraddress is included in both the first and second plurality of serveraddresses.
 23. The CDN for delivering content over the Internet asrecited in claim 21, wherein the first plurality of DNS solutions differfrom each other in that the first subset appear in a different order.24. The CDN for delivering content over the Internet as recited in claim21, wherein: the first DNS solution function produces a DNS solution forthe first domain; and the DNS solution is not the same as any of thefirst plurality of DNS solutions.
 25. The CDN for delivering contentover the Internet as recited in claim 21, wherein: a server address isincluded in both the first and second plurality of server addresses; andthe server address is assigned object requests as a result of being usedin the first and second plurality of DNS solutions.
 26. The CDN fordelivering content over the Internet as recited in claim 21, wherein thefirst subset is chosen from the third plurality of server addressesbased, at least in part, on processing power of the plurality of cachingservers indicated by the first subset.
 27. The CDN for deliveringcontent over the Internet as recited in claim 21, wherein the firstsubset includes the third plurality of server addresses.
 28. The CDN fordelivering content over the Internet as recited in claim 21, wherein thefirst and second DNS solution functions are performed with a DNS server.